Transformer connection for gaseous discharge tubes



April w. c. HALL, JR 2,Z3S),002

. TRANSFQRIE'R CONNECTION FOR GASEOUS DISCHARGE TUBES Filed Feb. 1Z5, 1939 INVENTOR may be lighted from a single unit and the power factor.

Patented Apr. 22, 1941 TRANSFORMER CONNECTION FORGASEOUS DISCHARGE TUBES Willard Cotton Hall, In, Los Angeles, calm, as-

signor to Lloyd Osborn James, Los Angeles,

Calif.

Application February it, rest, Serial No. 256,21

ion ire-n24) ,3 Claims.

This invention relates to gaseous conduction tube lighting transformers and a method of operation whereby to reduce the transformer bulk and cost per foot of tube operated on a single unit, increase the footage of tubing which improve In the majority of tube lighting installations several gaseous tubes are connected together in series in order to make use of higher voltage transformers than would be used if each tube were lighted from a single transformer. The higher voltage transformers are lower in cost per foot of tube operated and the operating efliciency is generally higher. Additional savings are effected in the wiring cost by combining v of two or more times the footage of tubing permissible with prior art devices.

In the manufacture of transformers of the type used for gaseous tube lighting it has been found that the output capacity may be doubled with an increase in cost of about 30% by doubling the secondary current. According to my invention a transformer is used having double the current output of that required by the individual tubes in the load, which current is split by an equalizer and caused to light two groups of tubes in a network which automatically regulates the current flow between the groups over a wide range of conditions.

It is a further object of this invention to provide an automatically balanced current divider arrangement which need not be accurately loaded as between the two tube groups. It is rare that in any given installation the tube lengths will divide up to make accurate balancing possible. It has been found with my invention that if the load on one side is less than the rated load, the transformer capacity may be used by adding tube footage to a corresponding overload to the other side within limits wide enough to permit of the use of the full capacity of the transformer under practically all commercial conditions.

In my copending application for patent, Serial No. 252,411, filed January 23, 1939, I disclosed a method and means or operating gaseous conduc= tion tubing by energy drawn at high power factor from the line. According to that invention, the tube load is caused to oscillate, apparently at or very close to resonance, with the inductance of the transformer. Under such conditions the power factor of the secondary circuit is very high, apparently close to unity, which improve= ment is reflected back into the primary circuit. It has also been found that the characteristic of the tube load is changed in some manner by these oscillations so that it is possible to use a very closely coupled transformer thus effecting further power factor improvement.

As tubes are added together in series to form high voltage loads, the capacity of the series falls, whereas as windings are added to the transformer secondary to provide the higher voltage the transformer inductance rises. It follows therefore, according to different transformer designs, there will be a certain range of secondary voltages most suited for the purpose. While secondary oscillation in the device is not critical, it has been found to be dependent on a magnetic shunt bridge of certain dimensions such as, will cause it to saturate early on each half cycle. This consideration and other design factors, notably the relationship between primary and secondary inductance for the high frequency component of the secondary current, impose restrictions on the design of transformers in the larger sizes.

It is an object of this invention to provide for the use of the method of my copending application mentioned by providing an inductance for oscillating with the capacitance of. the tube load which may be proportioned to match the lowered capacitance of the tube load in installations of the larger sizes.

. It has been found that the secondary circuit oscillation is dependent. on some action which adds increments of energy to the oscillating couple periodically at the resonant frequency. If this action is not present, the secondary voltage curve shows an initial oscillation upon the beginning of each half cycle which falls in a decremental curve to a straight line. In order to bring about the secondary circuit conditions of this invention it is an object to provide for the transference of energy from the commercial to the resonant frequency sufficient to maintain the high frequency oscillations: under widely varying load conditions. In accordance with the present invention, the transformer proper may be constructed with different degrees of coupling and with a greater latitude in design due to the fact that the equalizer itself forms the oscillating couple with the capacitance of the tube load.

It is known that in a resonating circuit the sum of the voltages across the capacitance and the inductance may be several times that of the impressed voltage. It is an object of this invention to take advantage of that phenomenon to develop voltages sufiicient to operate tube loads several times as long as that permissible with the typical shunt bridge transformer of the prior art. Accordingly the coupling of the transformer proper may be made very close and a good part of the duty of regulating current flow shifted to the resonating couple. In other words, we are here taking advantage of the fact that a resonating couple develops unity power factor, and a tube load when under resonance or near resonant conditions requires much less external regulation in spite of its negative resistance.

Further objects of the invention will be apparent from the following specification.

In the drawing Figure l. is a schematic illustration of the invention as applied with a step up transformer having a magnetic shunt bridge to provide a certain amount of leakage reactance. 1

Figures 2, 3, 4 and are oscillograms in which the primary voltage curve (b) is shown in each for reference purposes.

In Figure 2 is shown the secondary voltage curve of the transformer of Figure 1, indicated by (a), when operated with the normal rated load of tubing directly across the secondary terminals without the equalizers.

In Figure 3 the voltage curve across one of the tube groups of Figure 1 is shown and indicated by (c). Figure 4 shows the current curve through the same and indicated by (d).

The curve (e) of Figure 5 shows the voltage across the terminals of the secondary of the transformer proper of the device of Figure 1 when operated as shown in the View.

In the embodiment of the invention illustrated in Figure 1, the transformer proper, indicated by numeral I, is associated with two equalizin inductances 2 and 3, which are connected to two series connected groups of gaseous conduction tubes, represented by the single tubes 4 and 5. It is to be understood that each group may be made up of a single or a number of tubes, of a single or several types, in the manner customary in the art. The transformer proper includes the usual primary and secondary windings 8 and I on the main core legs and a high reluctance magnetic shunt bridge 8 to provide leakage reactance.

The secondary terminals of the transformer proper, indicated by 9 and III, are connected to mid-point taps II and I! of the inductances. The terminal 13 of the inductance 2 and the terminal l5 of the inductance 3 are connected to the tube group represented by tube 4. The terminal ll of the inductance 2 and the terminal I6 of the inductance 3 are connected to the tube group represented by the tube 5.

As regards the commercial frequency component of the current flow the inductances act as equalizers dividing the current between the two branches of the load. Either branch may be short circuited or opened, or the load may be unbalanced over a very considerable range with normal operating results.

The two tube groups and the inductances form a circuit for high frequency currents to a substantial degree independent of the transformer secondary. Thus when the proper inductance is used, consistent with the capacitance of the tube load this circuit will resonate, at any particular instant the high frequency component being additional to the low frequency current in one tube group and subtractive from the low frequency current in the other group.

As in the case of the invention disclosed in my copending application above stated, some factor, not as yet clearly identified, operates to apply increments of energy to the oscillating couple at the high frequency. Since there are numerous variables involved it is not practicable to advance specific instructions for the practice of this invention in terms of prior art transformer practice. I am therefore setting forth my theory of this device, in connection with the oscillograms in the drawing, whereby one skilled in the art may secure the results desired through empiric test and make such changes and modification as may be desired for different types of work.

It is to be understood however, that this theory is given for the purpose of elucidation only and may or may not be confirmed by subsequent research. The invention is therefore not to be limited in any manner by the theory or the necessary to maintain current flow once started.

As, to the theory of negative resistance, the behavior of tube light installations constructed ac- I cording to this invention, and the invention of my copending application above mentioned, indicates that the theory must be modified to account for the fact that it is possible to operate my transformers with very close coupling with tubes which are resonating, or under conditions very close thereto, with good regulation; the coupling being so close that the regulationis abnormal if the tubes'are not oscillating.

Accordingly it is pointed out that the resistance of a gas column under glow discharge conditions is a function of the ionization at any particular instant. If the ions disappear slower than they are formed, as they are known to. do, then if the current is oscillating around a certain medial value at a frequency sufficiently high for the residual 'ionization to be a material factor, the effective resistance will be less than the resistance for a steady current of the medial value. Furthermore, the resistance will change differently for a change of medial value of an oscillating current than for a steady state current of corresponding value. It is noted that there are many variables in gaseous tube operation and a complete explanation of the phenomenon may conceivably be quite involved. The evidence of my experiments indicates, however, that tubes operated on my transformers behave as though the negative resistance characteristic was greatly reduced and as might be expected from the theory above.

As to the excessive starting voltage thought to be necessary, I have discovered that tube loads may be operatedv without the application of voltage to start the discharge materially higher than that necessary to maintain it. In confirmation of this principle it is to be noted that the typical voltage curve across the terminals of a gaseous conduction lighting tube of the type used for electric signs and illumination'is very similar to the typical curve for pulse excitation of an oscillatory circuit and is not sufficient evidence of the presence of a higher striking voltage than the medial line of the curve. The neglected factor in this case being the elements of positive resistance in the gaseous discharge tube, which become'operative only after the tube has become conducting, and therefore are to be subtracted from the voltage of initiation.

, The negative resistance of the tubes constitutes the controlling factor in the design of the transformers of the prior art. Essentially they are current transformers and develop several times the full load voltage on open circuit test. When tubes connected to such transformers become hard or when the transformer is overloaded or otherwise operating under abnormal conditions, violent oscillations of random character and steep wave front surges occur due to the wide difference between the open circuit and full load potentials. Even under normal operating conditions when there is a difference of four hundred percent between these voltages the tubes evidence high frequency effects, give rise to radio inter-. ference and show other evidences of random behavior, which effects have generally been accepted as evidence of the instability of gaseous discharge tubes.

According to my theory and the results of my experiments, gaseous discharge tubes are far more stable in their behavior when operated as capacitances than has been heretofore believed and when operatedunder conditions effectively that of resonance at a frequency considerably higher than commercial frequency, the effects of negative resistance may be made to disappear to the extent that the coupling may be very close and the difference between the open circuit and full load potentials reduced to a negligible value. The excessive voltage for ignition now being absent, it is discovered that it is not necessary,very much to the contrary of the prior teachings of the art. I

In order to cause two gaseous conduction tubes or two series connected groups of tube to operate in parallel it is suflicient to connect in series with each of the circuit branches sufl'lcient impedance to prevent that branch which begins to conduct current first from lowering the voltage across the other branch to a value below the burning potential thereof Generally a small amount of inductance is sufficient. In the arrangement shown in Figure 1, whichever circuit 1 branch begins to conduct first will cause current to flow through one half of each of the equalizers. The equalizers then act as auto transformers and maintain the same voltage rise across the terminals of the other circuit branch. The inductance value necessary to insure stable parallel operation according to this arrangement is but a fraction of that of the transformer, in fact a wide selection of values is permissible including rent and potential conditions in a circuit including a standard shunt bridge transformer operated with the normal rated tube load on the secondary without the equalizers and with a tubeload three times as long operating through the equalizers.

Figure 2 shows the secondary voltage curve (a) of the transformer operating in the normal fashion with its full rated load in comparison with the primary voltage curve (b). A very decided lag is to be noted, th power factor being about 55%. The secondary voltage curve is seen to be sharply decremental and typical of the secondary voltage of high reactance gaseous tube lighting transformers.

Figure 3 shows the voltage curve across one tube group of the device as operated according to Figure 1 with the primary voltage curve (2)) shown for purposes of reference. This curve (0) is seen to be oscillatory, the amplitude of the high frequency component varying with the amplitude of the high frequency component of the current wave (11) of Figure 4.

In Figure 5 I show the voltage curve across the terminals of the transformer proper. This curve (e) is seen to lag much less behind the primary voltage than the secondary voltage of Figure 2, and also less than the voltage across the single tube branch as shown in Figure 3. The power factor as measured by the meters is 70%, it being apparent from this curve that the improvement is due to the action between the equalizers and the tube load, this phase displacement being what is to be expected if the tube load and the inductances formed an oscillating system at or close to resonance. The complex form' of this curve is a subject for future research, it being noted that in some manner the interaction between the oscillating system and the inductance of the transformer proper has to do with the energizing of the high frequency components. Not every combination which may be made will resonate, suitable combinations being matters of empiric determination.

While I have shown in Figure 1, a transformer with a magnetic shunt bridge, and illustrated the operation of the invention by means of curves taken with a standard type of leakage reactance transformer of the prior art, in practice the shunt bridge may be greatly reduced or in some cases eliminated altogether. The exact function of the bridge, other than to provide a certain amount of regulation, is not clearly understood, but it has been found that some action is necessary in order to sustain the secondary circuit oscillation. If the bridge be removed, new limitations in design appear and it becomes necessary to seek some combination of elements which will insure the building up of the high frequency component. It is to be understood, therefore, that this invention is not limited to the specific construction shown but may be variously modified and embodied in gaseous conduction tube lighting installations and devices andpracticed as a method of operation within the broad terms of the claims, such modification asthe substitution of some other element for the shunt bridge being so embraced.

The expression resonance" as used. in the claims is used in the broad sense of describing a steady state oscillatlon of the nature described in which the capacitance of the'tube load and the connected inductance function together to maintain an oscillatory condition under which the phase angle of the secondary voltage of the transformer is advanced,

Having thus described my invention, what I claim is:

1. In an electrical circuit for operating gaseous discharge tube loads, a plurality of units comprising inductance coils with endtaps, a central tap for each coil, a regulating transformer supplying step up voltages across the secondary thereof, means connecting the secondary of the transformer to the central tap of each inductance coil so as to place said coils at a difference of potential with respect to one another, each of said units having one of their end taps connected to an electrode of a different tube load and the other end tap of each unit having con nection with the other electrode of each tube load so as to supply current to each tube via of portions of both coil units.

2. In combination, a load consisting of a pair of lighting units, a pair of induction coils and a transformer having its primary connected to a supply of electrical energy at voltages and frequencies common to lighting circuits, each of said coils including end leads and a central tap, means connecting the central taps across the secondary of the transformer, means connecting one lead from each coil to one of the units and means connecting the other lead of each coil to the other unit to form a cross oscillating couple, said lighting units operating together as a complete whole or one without the other.

3. In a lighting system, a pair of lighting units, each unit having a pair of electrodes,'a pair of equalizing induction coils, each coil having end taps and a central tap, a power transformer having its primary connected to a source of electricity and its secondary to the central taps of said coils, means connecting one elec trode of one lighting unit and an electrode of the other unit to the terminals of one coil and the other electrodes of the units to the terminals of the other coil.

\WnLfiRD @OT'ION HALL, an. 

